For example, Patent Document 1 discloses an exhaust emission purifying system for a diesel engine equipped in an exhaust passage with a particulate filter (hereinafter referred to as “the PM filter”) for trapping particulate matter PM. This conventional system is designed to reduce the opening angle of an intake throttle valve and increase the opening angle of an EGR valve only when a judgment is made that the PM filter will not have excessively elevated temperature if the engine, during regeneration of the PM filter, comes into a deceleration operation state where fuel supply is stopped (fuel cut).
By exercising the above-mentioned control the conventional system suppresses lowering of and an excessive rise of the PM filter temperature if a diesel engine operation state comes into a deceleration operation state during regeneration of the PM filter. In this way, the conventional system attempts to satisfactorily continue the regeneration of the PM filter.
Including the above-mentioned document, the applicant is aware of the following document as a related art of the present invention.    [Patent Document 1] Japanese Laid-open Patent Application Publication No. 2005-201210    [Patent Document 2] Japanese Laid-open Patent Application Publication No. Hei 8-326524    [Patent Document 3] Japanese Laid-open Patent Application Publication No. 2003-129835    [Patent Document 4] Japanese Laid-open Utility Model Application Publication No. Sho 64-3017